Conventionally, in the field of manufacture of semiconductor devices, there has been known a plasma processing apparatus that processes a target substrate such as a semiconductor wafer by generating plasma within a hermetically sealed processing chamber. One example of such a plasma processing apparatus is a capacitively coupled plasma processing apparatus configured to generate plasma by applying a high frequency power between a lower electrode serving as a mounting table for mounting a target substrate thereon and an upper electrode provided to face the lower electrode. As one example, the capacitively coupled plasma processing apparatus may have a configuration in which a processing gas is supplied through a multiple number of gas discharge holes provided in the upper electrode, as in a shower device.
In the plasma processing apparatus having the aforementioned configuration, a surface of the upper electrode positioned to face a semiconductor wafer or the like may be formed of, e.g., a silicon electrode plate. In such a case, as a surface of a gas discharge hole provided in the upper electrode is eroded by plasma, a diameter of the gas discharge hole is enlarged. If the upper electrode having the gas discharge hole of the enlarged diameter continues to be used, electrons or ions flown into the gas discharge hole may reach a cooling plate on the side of a rear surface of the electrode, resulting in an abnormal electric discharge. Further, a gas within the gas discharge hole may be ionized by the electrons or ions, also resulting in an abnormal electric discharge. For the reason, the upper electrode is used only during a limited lifetime to prevent the abnormal electric discharge beforehand.
Moreover, it is known to arrange gas discharge holes in a labyrinth structure so as to prevent an abnormal electric discharge caused by the electrons or ions flown into the gas discharge holes. As one example, there has been known a labyrinth structure in which plates having a multiple number of fine holes are layered on top of each other and positions of the fine holes are deviated from each other (see, for example, Patent Document 1). Meanwhile, there has been known a labyrinth structure in which a large-diameter screw hole is provided above a gas discharge hole of a gas discharge plate and then a cylindrical screw having a hole at an eccentric position is screwed into the screw hole. Accordingly, the labyrinth structure can be formed by the gas discharge hole of the gas discharge plate and the eccentric hole of the screw (see, for example, Patent Document 2).
Patent Document 1: Japanese Patent Laid-open Publication No. 2007-5491
Patent Document 2: Japanese Patent Laid-open Publication No. H9-275093
As discussed above, conventionally, since the electrode plate needs to be replaced before the diameter of the gas discharge holes exceeds a certain size in order to suppress an abnormal electric discharge, a maintenance cycle is shortened, which results in a reduction of an operating rate or an increase of a running cost. Further, when a labyrinth structure is used to avoid such problems, a manufacturing cost may increase due to complication of the labyrinth structure. Furthermore, since conductance is decreased, a pressure within the gas discharge holes may increase, which may cause an abnormal electric discharge due to ionization of a processing gas. Especially, the problem of the occurrence of the abnormal electric discharge due to the ionization of the processing gas becomes serious in a recent plasma process in which a higher power tends to be used.